1. Field of the Invention
The present invention relates to a display device for displaying pictures in a form of multi-windows.
2. Description of the Prior Arts
A conventional multi-window picture display device is shown in FIG. 1. The device comprises a window memory 23 for-storing picture data to be displayed on the multi-window and a frame memory 22 for storing display data corresponding to picture elements of a CRT 21 acting as a display unit, whereby the picture data of the several windows read out from the window memory 23 are logically processed for the respective picture elements based on the registration signal by a raster operation unit (not shown) and the logically processed data is developed in the frame memory 22 as the display data, which are output to the CRT 21 synchronized with scanning timing signal so that the multi-windows A, B and C are displayed on the CRT 1 as shown in FIG. 1. In the example shown in FIG. 1, as a result of the logic operation of the windows A and B, the picture data of the window B is displayed and the result of the logical operation of the windows B and C is displayed as the picture data of the window C.
In the conventional device mentioned above, in order to display the picture data on the CRT 1, the content stored in the window memory 23 is subjected to the raster operation and the raster operated data is once developed in the frame memory 22. In turn the operated data is output to the CRT 1. Therefore, in case only the window C is moved to a separated area on the CRT 1, it is necessary to operate the raster operation on all of the contents in the windows A, B and C corresponding to the moving position and to develop the raster operated data in the frame memory 22, otherwise the windows can not be displayed on the CRT 1. Therefore, partly because the display output must be an indirect output, partly because non moved window A and B must be also operated by the raster operation, the multi-window display on the CRT 1 can not be performed with a high speed.